1.1
ABSTRACT The The obje object ctiv ive e of this this expe experi rime ment nt is to study study the the func functio tion n and and the the workin working g of shell shell and tube tube heat heat exchan exchanger ger.. For this this experi experimen ment, t, count counterercurrent heat exchanger is used. In counter flow heat exchangers, the two fluids flow against each other, maintaining a maximum temperature difference between the hot and cold streams which allows for maximum heat transfer. eat transfer and log mean temperature difference !"#T$% are calculated. In this experiment, we assume negligible heat transfer between the system and its surrou surroundi ndings ngs,, neglig negligibl ible e potent potential ial or kineti kinetic c energy energy change changes, s, consta constant nt specific specific heats, heats, and that the fluids are not undergoing undergoing any phase phase change. change. In this case, the heat transfer rate across a heat exchanger is usually expressed in the form & ' m(p )T. )T. Ther There e were ere also also calc calcul ulat atio ion n of "og "og #ean #ean Temperature $ifference !"#T$% and the formula is * "#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out % ! Th,out - Tc,in% The basic theory in this experiment is &h'&c, which the amount of heat transfer is e/ual to the amount of heat absorb.
1.2
INTRODUCTION eat 0xchangers are used to transfer heat from one fluid to another. The shell
and tube exchanger consists of a bundle of tubes with their axes parallel - much in the manner of soda straws in a carton - but supported at various points by baffles at right angles to the tube axes, which serve to keep the tubes fixed in space in a particular configuration, for example, with the axes spaced on e/uilateral triangles, or s/uares, etc. etc. (Kessler & Greenkorn,1999). #ost processes re/uire the heating or cooling of streams to produce a desired temperature before the stream can be fed to operations. In any heat exchanger there must be a fluid that re/uires a change in energy !heating or cooling% and a fluid that can provide that energy energy change. 1ne fluid is sent through a pipe on the inside of the heat exchange exchangerr while the other fluid fluid is sent through a pipe on the outside. outside. In this configuration, no mixing mixing of the hot and cold fluids needs needs to take place. This is very convenient for many processes, especially when product purity needs to be ensured. This arrangement also allows for large /uantities of heat to be transferred /uickly, and it is relatively r elatively easy to maintain consistent operating conditions. There There are three three princi principle ple means means of achiev achieving ing heat heat transf transfer er,, conduc conductio tion, n, convection, and radiation. radiation. eat exchangers run on the principles of convective and conductive heat transfer. transfer. 2adiation does occur occur in any process. process. owever, in most heat exchangers the amount of contribution from radiation is miniscule in comparison to that of convectio convection n and conduction. conduction. (onductio (onduction n occurs as the heat from the hot fluid passes passes through the inner pipe wall. To maximi3e maximi3e the heat transfer, transfer, the innerpipe wall should should be thin and very conductive. conductive. owever, owever, the biggest biggest contribution to heat transfer is made through convection. eat exchangers are typically classified according to flow arrangement. In the parallel-flow heat exchanger, the hot and cold fluids enter at the same end, flow in the same direction, and leave at the same end. In the counter-flow arrangement, the hot and cold fluids enter the heat exchanger at different ends and flow in opposite directions. 0ach fluid arrangement leads to different heat rates and the calculations are different accordingly !Incropera, !Incropera, DeWitt, Bergman & Lavine, 2!
eat exchangers are widely used in refrigeration, air conditioning, power plants, food processing, and many other applications. 4ll heat exchangers consist of two fluids at different temperatures separated by a conductive solid medium to allow heat transfer to occur between the two fluids and no mixing of the two fluids. #any types of heat exchangers exist5 plate and frame, shell and tube, counter flow, and parallel flow. eat exchangers can even have multiple passes of the fluid or fins to provide maximum heat transfer. The type of heat exchanger to provide the best heat transfer varies depending on the application. 6hell-and-Tube heat exchangers shown in Figure 7 and cross-current heat exchanger which is shown in Figure 8 are among the common types of heat exchangers. 4 basic schematic for a single pass shell-and-tube heat exchanger is shown in Figure 9. The stream to be cooled enters the tube side and is distributed amongst the tubes shown with red arrows. The stream that cools the li/uid is shown in blue enters on the shell-side and flows perpendicular to the tube bundle for maximum heat transfer. The shell-side flow passes around baffles placed around the tube bundle in order to increase both the residence time of the fluid around the tube bundle as well as to promote turbulence in order to maximi3e the efficiency of the heat exchanger.
Figure 1 : Shell and tube heat exchanger
Shell-Side Inlet
Figure 2 : Cr!! "l# heat exchanger
Shell-Side Outlet
Tube-Side Inlet
Tube-Side Outlet
Figure $ : Sche%atic " a Single&'a!! Shell&and&Tube (eat )xchanger #ith 'arallel&Fl# Cn"iguratin
For this experiment, counter-current heat exchanger is used. In counter flow heat exchangers, the two fluids flow against each other, maintaining a maximum temperature difference between the hot and cold streams which allows for maximum heat transfer. Figure : shows how the counter-current heat exchanger works
Figure * : The "l# " ht + cld #ater in cunter¤t heat exchanger
1.$
AI,S
7. To study the function and the working of shell and tube heat exchanger. 8. To calculate heat transfer and heat load with constant FT7. 9. To calculate "og #ean Temperature $ifference !"#T$% with constant FT7. :. To calculate heat transfer and heat load with constant FT8. ;. To calculate "og #ean Temperature $ifference !"#T$% with constant FT8. <. To study the working principle of counter flow heat exchanger. =. To study the effect of fluid temperature on counter flow heat exchanger performance. >. To study the effect of fluid flow rated on heat exchanger performance.
1.*
T()OR 4 heat exchanger is a piece of process e/uipment in which heat exchange
takes place between two fluids that enter and exit at different temperatures. The primary design objective of the e/uipment may be either to remove heat from a hot fluid or to add heat to a cold fluid. $epending upon the relative direction of fluid motion, shell-and-tube heat exchangers are classified as parallel flow, counter flow, cross flow. In parallel flow, the hot and cold fluids flow in the same direction and therefore enter the exchanger on the same end and exit the exchanger on the same end. In counter flow, the two fluids flow in opposite directions and thus enter the exchanger and exit the exchanger from opposite ends.
Figure : 'arallel and cunter "l# in Shell + Tube (eat )xchanger
The way that a heat exchanger works is hot water and cold water enter the exchanger, where the process of cold water gaining some heat and the hot water losing some takes place, before they both exit the exchanger. ?hat is actually happening is, the hot water is heating either the inside or the outside of the tubes in the exchanger, depending on where it is flowing, by what is known as convection. Then the heat is conducted through the tubes to the other side, either the outside or the inside, where it is then convection back into the cold water raising its temperature. (onvection is a mode of heat transfer that involves motion of some fluid that either absorbs heat from a source or gives heat to some surrounding.
For a heat exchanger that flows parallel or countercurrent then the coefficient of heat transfer is called the overall coefficient of heat transfer. It is calculated using the log mean temperature difference, which is found two different ways, depending on whether the flow is parallel or counter. 4 heat exchanger is a device by which thermal energy is transferred from one fluid to another. The types of heat exchangers to be tested in this experiment is counter-flow cheat exchanger. eat exchangers transfer heat from one working fluid to another. For instance, steam generators, feed water heaters, re heaters and condensers are all examples of heat exchangers found in nuclear power systems. The important /uantity in heat exchanger analysis is the total rate of heat transfer between the hot and cold fluid. 6everal different expressions for this heat transfer rate can be developed, relating the heat transfer rate to /uantities such as the inlet and outlet fluid temperatures and the overall heat transfer coefficient. ?hen these expressions are developed, care must be taken to ensure that the appropriate mean temperature expressions are used. 6everal assumptions can be made to simplify these expressions. ?e assume negligible heat transfer between the system and its surroundings, negligible potential or kinetic energy changes, constant specific heats, and that the fluids are not undergoing any phase change. The basic theory in this experiment is &h'&c, which the amount of heat transfer is e/ual to the amount of heat absorb. In this case, the heat transfer rate across a heat exchanger is usually expressed in the form & ' m" p #$. •
eat transfer rate for hot water,
•
eat transfer rate for cold water,
•
eat loss 2ate '
•
•
0fficiency '
Qh Qc
' mh (p )T ' mc (p )T
Q h− Q c
Qc x 100 Qh
$irt Factor, & ' @.; !&hA&c% where * & is heat exchanged m is flowrate (p is heat capacity )T is the temperature difference There were also calculation of "og #ean Temperature $ifference !"#T$%. "#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out % ! Th,out - Tc,in%
1.
A''ARATUS
The apparatus for this experiment is the 07;>( Tube eat 0xchanger. This apparatus has a tank with a heater inside to heat water to a specified temperature. The temperature setting is adjusted at the thermostat on the front panel. 1nce the water is heated to the desired temperature it is transferred by a water pump next to the tank. 1n the pump there is a knob which varies the pump pressure. ?hen using a volumetric flow rate above 8 "min the switch should be set to the highest pressure. The hot water is pumped through a pipe to an insulated tube for which heat will be exchanged. The actual heat exchange takes place in the i nsulated tubing for which cold water flows concentricity around the hot water tube in two different flow arrangements. These two arrangements, parallel and counter flow, can be changed by opening and closing certain valves within the network of hot and cold water tubing. 0ach flow arrangement is shown on a diagram located on the front panel. It is worthwhile to note that the temperature at cold-in changes to temperature at cold-out when a counter flow arrangement is used. The same situation applies to the temperature at cold-out, which changes to temperature cold-in for the counter flow. The other readings remain the same. The flow rates can be adjusted for both cold and hot water by turning the valve knobs on the right side of the panel. Thermometers are located at the inlet, exit and middle of the insulated heat exchanger tubing for both hot and cold water.
1./
'ROC)DUR)
1./.1 0eneral Start&u 'rcedure! : 7. 4 /uick inspection was performed to make sure that the e/uipment is in proper working condition. 8. 4ll valves were initially closed except B7 and B78. 9. ot tank was filled via a water supply hose connected to valve B8=. 1nce the tank is full, the valve was closed. :. The cold water tank was filled up by opening valve B8> and the valve was left opened for continuous water supply. ;. 4 drain hose was connected to the cold water drain point. <. #ain power was switched on. The heater for the hot water tank was switched on and the temperature controller was set to ;@o(. =. The water temperature in the hot water tank was allowed to reach the set point. >. The e/uipment was now ready to be run.
1./.2 0eneral Start&u 'rcedure! : 7. The heater was switched off. The hot water temperature was waited until it dropped below :@o(. 8. Cump C7 and pump C8 were switched off. 9. The main power was switched off. :. 4ll water in the process line was drained off. The water in the hot and cold water tanks were retained for next laboratory sessions. ;. 4ll valves were closed.
1./.$ Cunter¤t Shell + Tube (eat )xchanger 'rcedure! : 7. Deneral start-up procedures was performed. 8. The valves to counter-current 6hell E Tube eat 0xchanger arrangement was switched. 9. Cumps C7 and C8 were switched on. :. Balves B9 and B7: were adjusted and opened to obtain the desired flowrates for hot water and cold water streams, respectively. ;. The system was allowed to reach steady state for 7@ minutes. <. FT7, FT8, TT7, TT8, TT9 and TT: were recorded. =. Cressure drop measurements for shell-side and tube side were recorded for pressure drop studies. >. 6teps : to = were repeated for different combinations of flowrate FT7 and FT8. . Cumps C7 and C8 were switched off after the completion of experiment.
1.
R)SU3TS
0xperiment 4 * (ounter-current 6hell E Tube eat 0xchanger !constant FI 7%. FI 1
FI 2
TT 1
43',5 43',5 46C5 7@ 8 :9.; 7@ : 9.8 7@ < 9<.> 7@ > 9;.@ 7@ 7@ 9:.= Table 7 * (ounter-current
TT 2
TT $
TT *
D'T 1
D'T 2
46C5 46C5 46C5 4%%(2O5 4%%(2O5 9@.: :=.; :.8 = 7>
[email protected] :=.@ :.= 7@9 89 8.; :<.9 :.= 7@@ <; 8. :;.< :>. 7 79@ 9@.; ::.> :>. 8 7@ 6hell E Tube eat 0xchanger with constant FI 7
0xperiment G * (ounter-current 6hell E Tube eat 0xchanger !constant FI 8%. FI 1
FI 2
TT 1
43',5 43',5 46C5 8 7@ 97. : 7@ 98.; < 7@ 99.: > 7@ 9:.9 7@ 7@ 9;.@ Table 8 * (ounter-current
1.7
CA3CU3ATIONS
)8')RI,)NT 1 :
TT 2
TT $
TT *
D'T 1
D'T 2
46C5 46C5 46C5 4%%(2O5 4%%(2O5 9@.: 9=.> :>.= ; 7; 9@.; :8. :>.> ; 7: 9@.; ::.7 :.7 ; 79 9@.< ::.; :.= <@ 78 9@.> :;.: :.> >8 77 6hell E Tube eat 0xchanger with constant FI 8
7. (alculation 1n eat Transfer and heat load !constant FT7% and (alculation of "og #ean Temperature $ifference !"#T$% *
•
Qh
eat transfer rate for hot water, Qh
L
' 7@.@
1 m
x
min
3
' mh (p )T kg
1 min
x
1000 L
x >>.7> m
60 s
3
J kg.C
x :7=;
!:9.;-9@.:% H( ' @@=.<= ? •
eat transfer rate for cold water, Qc
' 8.@
L min x
3
1m
1000 L
Qc
' mc (p )T kg
1 min
x
60 s
x ;.<= m
3
x :7>9
J kg.C x
!:.8-:=.;% H( ' 89<.@7 ? •
eat loss 2ate ' Q h −Q c
Q h− Q c
' @@=.<=-89<.@7
' >==7.<< ?
•
0fficiency
'
Qc x 100 Qh 236.01
'
9007.67
x 100
' 8.<8 •
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% !Th,out- Tc,in%
( 43.5− 49.2 )−( 30.4− 47.5 ) ( 43.5 − 49.2) ' ¿ ( 30.4 − 47.5) '
[email protected]>J(
x
•
$irt Factor, & ' @.; !&hA&c% ' @.; !@@=.<=A89<.@7% ' :<87.>:
8. (alculation 1n eat Transfer and heat load !constant FT7% and (alculation of "og #ean Temperature $ifference !"#T$% * •
eat transfer rate for hot water,
7@.@
3
L min x
Qh
' m% " p #$ kg
1 min
1m
x
1000 L
60 s
x >>.7> m3 x :7=;
J kg.C x !9.8-
[email protected]% H( ' <8;=.8: ? •
eat transfer rate for cold water,
' :.@
L min x
3
1m
1000 L
1 min
x
60 s
Qc
mc " p #$ kg
x ;.<= m
3
x :7>9
J kg.C x !:.=-
:=.@% H( ' =:.<= ? •
Q h− Q c
eat loss 2ate ' ' <8;=.8:-=:.<= ' ;;@=.;= ?
•
0fficiency 749.67
'
•
6257.24
'
x 100
Qc x 100 Qh
' 77.>
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 39.2 −49.7 )−(30.1 −47.0 ) (39.2− 49.7 ) ' ¿ ( 30.1− 47.0 ) ' -79.:;J( •
$irt Factor, & ' @.; !&hA&c% ' @.; !<8;=.8:A=:.<=% ' 9;@9.:<
9. (alculation 1n eat Transfer and heat lost !constant FT7% and (alculation of "og #ean Temperature $ifference !"#T$% * •
eat transfer rate for hot water,
7@.@
3
L min x
1m
1000 L
Qh
' m% " p #$ kg
1 min
x
60 s
x >>.7> m
3
x :7=;
J kg.C x !9<.>-
8.;% H( ' ;@7.;: ? •
eat transfer rate for cold water,
' <.@
L min x
3
1 min
1m
1000 L
x
:<.9% H( ' 7:7<.@< ? •
eat loss 2ate ' ' ;@7.;:-7:7<.@<
Q h− Q c
60 s
Qc
mc " p #$ kg
x ;.<= m3 x :7>9
J kg.C x !:.=-
' 9<@9.:> ?
•
0fficiency
'
•
'
1416.06 x 100 5019.54
Qc x 100 Qh
' 8>.87
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 36.8 −49.7 )−( 29.5− 46.3) (36.8 −49.7 ) ' ¿ ( 29.5 −46.3 ) ' -7:.=
$irt Factor, & ' @.; !&hA&c% ' @.; !;@7.;:A7:7<.@<% ' 987=.>
:. (alculation 1n eat Transfer and heat lost !constant FT7% and (alculation of "og #ean Temperature $ifference !"#T$% * •
eat transfer rate for hot water,
7@.@
L min x
3
' m% " p #$ kg
1 min
1m
1000 L
Qh
x
60 s
x >>.7> m
3
8.% H( ' 9;@<.>@ ? •
eat transfer rate for cold water,
Qc
mc " p #$
x :7=;
J kg.C x !9;.@-
' >.@
L min x
3
1 min
1m
1000 L
x
60 s
kg
x ;.<= m3 x :7>9
J kg.C x !:>.-
:;.<% H( ' 7>98.;; ? •
Q h− Q c
eat loss 2ate ' ' 9;@<.>@-7>98.;; ' 7<=:.8; ?
•
0fficiency 1832.55
'
•
3506.80
'
x 100
Qc x 100 Qh
' ;8.8>
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 35.0 −48.9 )−(29.9 −45.6 ) (35.0 −48.9 ) ' ¿ ( 29.9 −45.6 ) ' -7:.=>J( •
$irt Factor, & ' @.; !&hA&c% ' @.; !9;@<.>@A7>98.;;% ' 8<<.<>
;. (alculation 1n eat Transfer and heat lost !constant FT7% and (alculation of "og #ean Temperature $ifference !"#T$% *
•
eat transfer rate for hot water,
7@.@
L min x
3
' m% " p #$ kg
1 min
1m
1000 L
Qh
x
x :7=;
J kg.C x !9:.=-
x ;.<= m3 x :7>9
J kg.C x !:>.-
x >>.7> m
3
60 s
9@.;% H( ' 8>>=.< ? •
eat transfer rate for cold water,
' 7@.@
L min x
3
1m
1000 L
Qc
1 min
x
60 s
mc " p #$ kg
::.>% H( ' 8>:<.@7 ? •
Q h− Q c
eat loss 2ate ' ' 8>>=.<-8>:<.@7 ' :7.; ?
•
0fficiency 2846.01
'
•
2887.96
'
x 100
Qc x 100 Qh
' >.=;
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 34.7 − 48.9 )−( 30.5− 44.8) (34.7 −48.9 ) ' ¿ ( 30.5 −44.8 ) ' -7:.8;J( •
$irt Factor, & ' @.; !&hA&c% ' @.; !8>>=.
:<.@7% ' 8><<.
)8')RI,)NT 2 : 7. (alculation 1n eat Transfer and heat lost !constant FT8% and (alculation of "og #ean Temperature $ifference !"#T$% * •
eat transfer rate for hot water,
8.@
L min x
3
Qh
' m% " p #$ kg
1 min
1m
1000 L
x
x >>.7> m
3
60 s
x :7=;
J kg.C x !97.-
9@.:% H( ' 8@<.8> ? •
eat transfer rate for cold water,
' 7@.@
L min x
3
1m
1000 L
Qc
1 min
x
60 s
mc " p #$ kg
x ;.<= m3 x :7>9
J kg.C x !:>.=-
9=.>% H( ' =;<<.87 ? •
Q h− Q c
eat loss 2ate ' ' 8@<.8>-=;<<.87 ' -=9;.9 ?
•
0fficiency 7566.21
'
•
206.28
'
x 100
Qc x 100 Qh
' 9<<=.9
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 31.9 −48.7 )−( 30.4−37.8 ) (31.9− 48.7 ) ' ¿ ( 30.4 −37.8 ) ' -77.:
$irt Factor, & ' @.; !&hA&c% ' @.; !8@<.8>A=;<<.87% ' 9>><.8;
8. (alculation 1n eat Transfer and heat lost !constant FT8% and (alculation of "og #ean Temperature $ifference !"#T$% * •
eat transfer rate for hot water,
:.@
L min x
3
Qh
' m% " p #$ kg
1 min
1m
1000 L
x
x >>.7> m
x :7=;
3
60 s
J kg.C x !98.-
9@.;% H( ' <<@.7@ ? •
eat transfer rate for cold water,
' 7@.@
L min x
3
1 min
1m
1000 L
x
:8.% H( ' :@;.:= ? •
eat loss 2ate ' ' <<@.7@-:@;.:= ' -9:9;.9= ?
Qc
Q h− Q c
60 s
mc " p #$ kg
x ;.<= m
3
x :7>9
J kg.C x !:>.>-
•
0fficiency
'
•
Qc x 100 Qh
'
4095.47 x 100 660.10
' <8@.:9
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 32.9 −48.8 )−(30.5 −42.9 ) (32.9− 48.8 ) ' ¿ ( 30.5 −42.9 ) ' -7:.@>J( •
$irt Factor, & ' @.; !&hA&c% ' @.; !<<@.7@A:@;.:=% ' 89==.=
9. (alculation 1n eat Transfer and heat lost !constant FT8% and (alculation of "og #ean Temperature $ifference !"#T$% * •
eat transfer rate for hot water,
<.@
L min x
3
x
60 s
' m% " p #$ kg
1 min
1m
1000 L
Qh
x >>.7> m
3
9@.;% H( ' 77<.:: ? •
eat transfer rate for cold water,
Qc
mc " p #$
x :7=;
J kg.C x !99.:-
' 7@.@
L min x
3
1 min
1m
1000 L
x
60 s
kg
x ;.<= m3 x :7>9
J kg.C x !:.7-
::.7% H( ' 9:=@.=: ? •
Q h− Q c
eat loss 2ate ' ' 77<.::-9:=@.=: ' -88=:.9@ ?
•
0fficiency 3470.74
'
•
1196.44
'
x 100
Qc x 100 Qh
' 8@.@
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 33.4 − 49.1 )−( 30.5 − 44.1) (33.4 −49.1 ) ' ¿ ( 30.5 −44.1 ) ' -7:.<8J( •
$irt Factor, & ' @.; !&hA&c% ' @.;!9:=@.=:A77<.::% '8999.;
:. (alculation 1n eat Transfer and heat lost !constant FT8% and (alculation of "og #ean Temperature $ifference !"#T$% *
•
eat transfer rate for hot water,
>.@
L min x
3
Qh
' m% " p #$ kg
1 min
1m
1000 L
x
x >>.7> m
3
60 s
x :7=;
J kg.C x !9:.9-
9@.<% H( ' 8@9;.98 ? •
eat transfer rate for cold water,
' 7@.@
L min x
3
1m
1000 L
Qc
1 min
x
60 s
mc " p #$ kg
x ;.<= m3 x :7>9
J kg.C x !:.=-
::.;% H( ' 9<@.;= ? •
Q h− Q c
eat loss 2ate ' ' 8@9;.98-9<@.;= ' -7;=:.8; ?
•
0fficiency 3609.57
'
•
2035.32
'
x 100
Qc x 100 Qh
' 7==.9;
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out % ! Th,out - Tc,in%
( 34.3 −49.7 )−( 30.6− 44.5) (34.3 −49.7 ) ' ¿ ( 30.6 −44.5 ) ' -7:.<9J( •
$irt Factor, & ' @.; !&hA&c% ' @.; [email protected]<@.;=% ' 7@<.:;
;. (alculation 1n eat Transfer and heat lost !constant FT8% and (alculation of "og #ean Temperature $ifference !"#T$% * •
eat transfer rate for hot water,
7@.@
L min x
3
1m
1000 L
Qh
' m% " p #$ kg
1 min
x
x :7=;
J kg.C x !9;.@-
x ;.<= m3 x :7>9
J kg.C x !:.>-
x >>.7> m
3
60 s
9@.>% H( ' 8>>=.; ? •
eat transfer rate for cold water,
' 7@.@
L min x
3
1m
1000 L
Qc
1 min
x
60 s
mc " p #$ kg
:;.:% H( ' 9@;:.8; ? •
eat loss 2ate '
Q h− Q c
' 8>>=.;-9@;:.8; ' -7<<.9 ?
•
0fficiency 3054.25
'
•
2887.95
'
x 100
Qc x 100 Qh
' 7@;.=<
"#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out% ! Th,out - Tc,in%
( 35.0 −49.8 )−(30.8 −45.4 ) (35.0 −49.8 ) ' ¿ ( 30.8 −45.4 )
' -7:.=@J(
•
$irt Factor, & ' @.; !&hA&c% ' @.; ! 3054.25 A
2887.95
%
' 8=7.7
1.9
DISCUSSIONS In this experiment of shell and tube heat exchanger particular apparatus,
water is used as both the hot and cold fluid. The purpose of this heat exchanger is to cool a hot stream. (ooling water flows through the outer pipe !the shell%, and hot water flows through the inner pipe on the inside. eat transfer occurs in both directions5 the hot water is cooled, and the cooling water is heated. This arrangement is called a Kshell-and-tubeL heat exchanger. There are many other forms of heat exchangers5 most notably, the double-pipe heat exchanger. In this arrangement, a cold fluid flows through a pipe in the center of the apparatus and is heated by a hot fluid on the outside of that pipe. The hot water used in the shell-and-tube heat exchanger is produced by means of a double-pipe heat exchanger. The discharge from the shell of the shell-and-tube heat exchanger is circulated through the inner pipe of the double pipe heat exchanger. "ow-pressure steam condenses on the outside of the pipe, heating the water before it enters the tubes of the shell-and-tube heat exchanger. For this experiment, counter-current heat exchanger is used. In counter flow heat exchangers, the two fluids flow against each other, maintaining a maximum
temperature difference between the hot and cold streams which allows for maximum heat transfer. In this experiment we are able to determine the value of heat load !&h and &c% besides to calculate the "#T$. ?e assume negligible heat transfer between the system and its surroundings, negligible potential or kinetic energy changes, constant specific heats, and that the fluids are not undergoing any phase change. In this case, the heat transfer rate across a heat exchanger is usually expressed in the form & ' m(p )T. •
eat transfer rate for hot water,
Qh
' mh (p )T
•
eat transfer rate for cold water,
Qc
' mc (p )T
•
eat loss 2ate '
•
0fficiency '
Q h− Q c
Qc x 100 Qh
where * & is heat exchanged m is flowrate (p is heat capacity )T is the temperature difference
Crocess fluid streams may contain suspended matters or dissolved solids. ?hen such a fluid flows through a heat exchanger over a long period of time, deposition of the tube surfaces and shell surfaces occurs. The surfaces may also be corroded by fluid slowly and the resulting corrosion products also get deposited on the surface. Formation of the deposit on a heat transfer surface is called fouling and the heat transfer resistance offered by the deposit is called the fouling factor or dirt factor commonly denoted by 2d. the dirt factor cannot be estimated. It can only be determined from the experimental data on heat transfer coefficient of a fouled exchanger and a clean exchanger of similar design operated at i dentical conditions. From the e/uation to gain $irt factor, & is refer to &h or &c. Gut if error happened, take average value of M, by calculating & ' @.; !&A&(%
•
$irt Factor, & ' @.; !&hA&c%
There were also calculation of "og #ean Temperature $ifference !"#T$%. "#T$, )T"# ' +! Th,in Tc,out% !Th,out Tc,in% ln+! Th,in Tc,out % ! Th,out - Tc,in%
The basic theory in this experiment is &h'&c, which the amount of heat transfer is e/ual to the amount of heat absorb. In this experiment, the value of &h is not the exact value as &c because of some errors occur during this experiment. For example, heat loss to the surroundings. Cresently, the heat exchanger has no insulation and the ambient room temperature has a large effect on the results obtained in this experiment and the reading affects the calculations too.
1.16
CONC3USION The heat exchanger apparatus follows the basic laws of thermodynamics and
this can be shown experimentally. From the other experiments that hold flow rates constant or vary the flow rates, it is clear that the First "aw of Thermodynamics and conservation of energy applies to the heat exchanger apparatus. The basic theory in this experiment is &h'&c, which the amount of heat transfer is e/ual to the amount of heat absorb. 4lthough the value of &h obtained in this experiment is slightly different with &c, this might due to some errors occur during this experiment and the recommendations were made to improve this experiment.
1.11
R)CO,,)NDATIONS For this experiment of shell and tube heat exchanger, it is recommended that
the heat exchanger be well insulated in order to reduce the heat loss to the surroundings. Cresently, the heat exchanger has no insulation and the ambient room temperature has a large effect on the results obtained in this experiment. 4part from that, the flowrate measure during this experiment must be taken accurately. The eyes must be perpendicular to the scale of the flow meter so that the readings will be more accurate. $uring the experiment, it is recommended that the readings such as FT7, FT8, $CT7, $CT8 and temperature must be taken when the system is stabili3ed and reach its steady state. If the readings were taken when the system are not in stabili3ed condition, error might be occur. Then this will affect the readings and also the calculations. Next, to improve the system of shell and tube heat exchanger, it is recommended that the shell and tube heat exchanger have alert sign or alarm that
can give a sign to the engineer who handles the e/uipment to take the readings at the correct time in order to get accurate readings. 6o that, this would help in reducing the inaccuracy of the measurements in the future. "astly, the water to the tube side should be the first and last flow rate to be turned on. The steam should be turned on only after the water is flowing through the tube side and the water should be turned on only after the steam has been turned on so that the tube and shell heat exchanger can operates more effectively.
1.12
R)F)R)NC)S
7% Oessler, $.C., Dreenkorn, 2.4. !7%. #omentum, eat, and #ass Transfer Fundamentals, New Pork * #arcel $ekker Inc., pp !=<>->8>%. 8% olman, Q.C. !7>7%, eat Transfer, ;th 0dition, New Pork * #cDraw ill, pp !:9=:<=%. 9% http*www.ejbowman.co.ukproducts6hellandTubeeat0xchangers.html retrieved on :.:.8@7;. :% http*www.alfalaval.comabout-usour-companykey-technologiesheattransfershell-and-tube-heat-exchangerspagesshell-and-tube-heat-exchanger.aspx retrieved on :.:.8@7;. ;% http*www.thermopedia.comcontent7787 retrieved on :.:.8@7; <% #c(abe, ?."., 6mith, Q.(., #arriott, C. !7>;%, Mnit 1perations of (hemical 0ngineering, :th 0dition, #cDraw-ill.
=% Incropera, $e?itt, Gergman, "avine. !8@@=%, Introduction to eat Transfer, ;th 0dition, New Pork * Qohn ?iley.